Communications system reconfigurable with reduced network configuration data

ABSTRACT

In a reconfigurable communications system, circuit status bits are stored in a first matrix of rows associated respectively with predefined network configurations and columns associated, respectively, with predefined circuit configurations. Destination status codes are stored in a second matrix of rows associated respectively with the circuit configurations and columns associated, respectively, with switching nodes of the system. Each circuit configuration comprises one or more transmission links, and each circuit status bit stored in each column of the first matrix pattern indicates the presence or absence of the circuit configuration associated with that column. Each destination status code indicates the presence or absence of transmission links from each switching node to possible destination nodes. In response to a manual command, the circuit status bits stored in one of the rows of the first matrix are respectively multiplied with those of the destination status codes stored in each column of the second matrix. Then multiplied binary values are summed, so that network configuration data is derived with respect to a desired network configuration, which is then transmitted to the switching nodes to reconfigure the system. In a modified embodiment, a difference is detected between the network configuration data successively derived with respect to previous and most recent network configurations and transmitted as network configuration signals to the switching nodes.

This application is a division of application Ser. No. 07/676,971, filed Mar. 29, 1991 now U.S. Pat. No. 5,307,465.

BACKGROUND OF THE INVENTION

The present invention relates generally to communications systems and more specifically, to a reconfigurable communications system in which switching nodes are interconnectable by transmission links according to network configuration signals supplied from a network control center.

According to conventional reconfigurable communications systems, the network control center is provided with a memory in which network Configuration data are stored in a matrix pattern of rows and columns so that the rows correspond respectively to predefined network configurations and the columns correspond respectively to switching nodes of the system. When the system traffic is imbalanced due to varying user's communications needs or a varying community of interest, a command is entered to a management console specifying one of the predefined network configurations which is selected as the best for balancing the system's traffic. The network configuration data corresponding to the selected configuration is retrieved from the memory and sent to the switching nodes to reconfigure the network.

However, there is a wide range of user's needs. To meet the varying user's demands many network configurations must be predefined, and, hence, a large capacity memory is required for storing corresponding network configuration data to achieve a high level of flexibility. In addition, during the network reconfiguration phases, each switching node clears all of its static connections in response to the signal from the network control center before it establishes new static connections. However, this increases the burden of the controller of each switching node.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to reduce the amount of data to be stored in a network management memory necessary for network configuration.

This object is obtained by factoring network configuration data into first component data and second component data, storing the first and second component data into memory and multiplying appropriate first and second component data to obtain desired network configuration data for transmission to switching nodes.

Specifically, the present invention provides a communications system having a plurality of switching nodes, each being capable of establishing and removing relatively static connections between transmission links in response to network configuration signals and of establishing relatively dynamic connections through the established static connections in response to information pertaining to call-by-call connection requests from user terminals, wherein the system includes a network control center having a management console to which a command is entered as an indication of a desired one of a plurality of predefined network configurations. Circuit status bits (first component data) are stored in a first matrix pattern of rows associated respectively with the predefined network configurations and columns associated respectively with predefined circuit configurations, and destination status codes (second component data) are stored in a second matrix pattern of rows associated respectively with the circuit configurations and columns associated respectively with the switching nodes, each of the circuit configurations comprising one or more transmission links. Each of the bits stored in each column of the first matrix pattern indicates the presence or absence of the circuit configuration associated with the column of the first matrix pattern, and each of the codes indicates the presence or absence of transmission links from each switching node to possible destination nodes. In response to a command entered to the management console, the binary values of the circuit status bits stored in one of the rows of the first matrix pattern are respectively multiplied with binary values of the destination status codes stored in each column of the second matrix pattern, and the multiplied binary values are summed so that network configuration data is derived with respect to a desired network configuration. The network configuration data is then transmitted to the switching nodes to reconfigure the system.

Another object of this invention is to reduce the burden taken by each switching node of the system during a network reconfiguration phase.

This object is attained by detecting a difference between first and second network configuration data corresponding respectively to an existing network configuration and a new network configuration which is currently nonexistent, and transmitting the difference as a network configuration signal to switching nodes.

More specifically, the present invention provides a communications system having a plurality of switching nodes, each being capable of establishing and removing relatively static connections between transmission links in response to network configuration signals and of establishing relatively dynamic connections through the established static connections in response to information pertaining to call-by-call connection requests from user terminals, wherein the system includes a network control center having a management console to which a command is entered as an indication of a desired one of a plurality of predefined network configurations. According to a second aspect of the present invention, circuit status bits are stored in a first matrix pattern of rows associated respectively with the predefined network configurations and columns associated respectively with predefined circuit configurations, and destination status codes are stored in a second matrix pattern of rows associated respectively with the circuit configurations and columns associated respectively with the switching nodes. Each of the circuit configurations comprises one or more transmission links, and each of the bits stored in each column of the first matrix pattern indicates the presence or absence of the circuit configuration associated with the column of the first matrix pattern, and each of the codes indicate the presence or absence of transmission links from each switching node to possible destination nodes. In response to a command entered in the management console, the circuit status bits are retrieved from one of the rows of the first matrix pattern and the destination status codes are retrieved from each column of the second matrix pattern, and the binary values of the retrieved circuits status bits are multiplied with the binary values of the retrieved destination status codes and the multiplied binary values are summed to derive network configuration data associated with a first network configuration. In response to a second command entered to the management console, a similar process is repeated to derive network configuration data associated with a second network configuration. A difference is detected between the network configuration data successively derived with respect to the first and second network configurations and transmitted as network configuration signals to the switching nodes.

According to a modification, the circuit status bits are retrieved from each row of the first matrix pattern and the destination status codes are retrieved from each column of the second matrix pattern. The binary values of the retrieved circuits status bits are respectively multiplied with the binary values of the retrieved destination status codes, the multiplied binary values being summed together to derive network configuration data for each of the predefined network configurations. The network configuration data derived for the predefined network configurations are stored into a memory. In response to a command entered to the console, a pair of first and second network configuration data are retrieved from the memory, with the first network configuration data being associated with a new network configuration and the second network configuration data being associated with a previous network configuration. A difference between the network configuration data of the pair is detected and transmitted as the network configuration signals to the switching nodes.

According to further modifications, a plurality of network configuration data corresponding respectively to distinct network configurations are stored in a memory, and first and second network configuration data corresponding respectively to an existing network configuration and a new network configuration are retrieved from the memory. A determination is made if there is a difference between the first and second network configuration data. The second network configuration data is sent to switching nodes as network configuration signals if it is determined that there is a difference between the first and second network configuration data. A code indicative of such a difference may be detected and transmitted, instead of the second network configuration data, to only those switching nodes requiring network reconfiguration.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described in further detail with reference to the accompanying drawings, in which:

FIG. 1 shows in block form a communications network having a network control center according to the present invention;

FIG. 2 shows a list of circuit status bits stored in memory in a matrix format tabulated according to network configurations and circuit configurations;

FIG. 3 shows a list of destination status codes stored in the memory in a matrix format tabulated according to circuit configurations and switching nodes;

FIGS. 4A through 4G show the contents of the destination status codes of respective circuit configurations stored in the memory in a matrix format tabulated according to source and destination switching nodes;

FIG. 5 shows in flowchart form a sequence of programmed instructions performed by the controller of FIG. 1 according to an embodiment of the present invention;

FIG. 6 shows programmed instructions performed by the controller according to a modified embodiment of the present invention;

FIGS. 7A through 7E show in matrix form network configuration data of predefined network configurations stored in locations of the memory accessible as a function of network identifiers and switching node identifiers;

FIG. 8A shows in flowchart form a sequence of programmed instructions performed by the controller according to a second embodiment of the present invention;

FIG. 8B shows in flowchart form a sequence of modified instructions of the second embodiment of the present invention;

FIG. 9A shows in flowchart form a sequence of modified program instructions of the second embodiment; and

FIG. 9B shows in flowchart form a sequence of further modified program instructions of the second embodiment.

DETAILED DESCRIPTION

Referring now to FIG. 1, there is shown a communications network according to the present invention. The network is made up of a plurality of switching nodes 2 for servicing user's data terminal 1. For purposes of disclosure, five switching nodes 2₁ through 2₅ are shown interconnected by full-duplex transmission links 3₁ through 3₉. A network controller 4 is provided for setting up relatively static connections between switching nodes of the network by entering commands at a management console 6.

Each switching node has a digital switching matrix that responds to signaling information from the user terminals pertaining to call-by-call connection requests by establishing a circuit-switched connection or a packet-switched connection, depending on the mode of operation of the network. To permit instant reconfiguration of the network, each switching node has a digital cross-connect function that responds to a network configuration signal from the network control center 4 by establishing a relatively static connection to one or more switching nodes.

Network control center 4 is made up of a network controller 5, a management console 6, a network management memory 7, and transmitters 8₁ ˜8₅ which are associated respectively with switching nodes 2₁ ˜2₅ through respective control channels 9. As will be described, when a traffic imbalance occurs in the network, manual command input is supplied from console 6 to controller 5, indicating a network identifier (m) which reconfigures the original configuration to eliminate the traffic imbalance (where m is an identifier uniquely indicating a particular network configuration). In response to this signal, controller 5 searches through the memory 7 and generates network configuration data (N_(mn)) for each switching node 2_(n) and applies it to a corresponding transmitter 8_(n), in which it is converted into a format indicating a sequence of destination nodes or link identifiers followed by a 0 or a 1 indicating respectively the provisioning or disconnecting of a link to a destination.

The communications network of this invention comprises a plurality of circuit configurations. For purposes of disclosure, seven different circuit configurations and five different network configurations are predetermined, and more than one circuit configuration is chosen from the seven circuit configurations for each of the five network configurations.

In the network management memory 7 is stored a circuit configuration table 10 as shown in FIG. 2. Circuit configuration table 10 is a list of circuit status bits (E_(mp)), where p identifies a particular circuit configuration. Each circuit status bit E_(mp) is either a binary 1 indicating the presence of a circuit configuration or a binary 0 indicating the absence of any circuits. A unique set of E_(mp) bits is assigned to each network configuration. A network configuration m=1, for example, is assigned a set of bits E₁₁, E₁₂, E₁₃, E₁₄, E₁₅, E₁₆ and E₁₇, which are respectively, "1", "1", "0", "0", "0", "0" and "0". Therefore, network configuration m=1 is made up of circuit configurations p=1 and p=2, and a network configuration m=2 is assigned a set of bits circuit status bits E₂₁, E₂₂, E₂₃ , E₂₄, E₂₅, E₂₆ and E₂₇, which are respectively, "1", "0", "1", "0", "1", "0" and "0". Therefore, network configuration m=2 is made up of circuit configurations p=1, p=3 and p=5.

As shown in FIG. 3, the circuit configurations are represented by a destination status channel table 11 which is stored in the network management memory 7. Each of the seven circuit configurations is identified by a set of destination status codes C_(pn) which correspond respectively to switching nodes 2_(n). For example, circuit configuration p=1 is given by a set of codes C₁₁, C₁₂, C₁₃, C₁₄ and C₁₅ and circuit configuration p=2 is represented by a set of codes C₂₁, C₂₂, C₂₃, C₂₄ and C₂₅.

Details of the destination status codes will be described with reference to FIGS. 4A˜4G.

Circuit configuration p=1 is formed by link 3₂ between nodes 2₁ and 2₂ and link 3₃ between nodes 2₂ and 2₄ (FIG. 4A). A list of codes C_(1n) (where n=1, 2, . . . 5) is given in a table 12A which indicates the destination status of circuit configuration p=1. A binary 1 in the destination status codes indicates the presence of a link from a source node to a destination node which is specified by the position of the bit in the code and a binary 0 indicates the absence of such a link. In this case, code C₁₁ for source node 2₁ is "01000", indicating that there is a link available between nodes 2₁ and 2₂. Likewise, code C₁₂ for source node 2₂ is represented by "10010", indicating that links are available between node 2₂ and node 2₁ and between nodes 2₂ and 2.sub. 4. Code C₁₄ for source node 2₄ is represented by "01000", indicating that a link is available between nodes 2₄ and 2₂. The other codes C₁₃ and C₁₅ are represented by all zeros indicating no links are available for switching nodes 2₃ and 2₅.

In like manner, circuit configuration p=2 is formed by link 3₇ between nodes 2₄ and 2₅ and link 3₈ between nodes 2₃ and 2₅ (FIG. 4B). A list of codes C_(2n) is given in table 12B, indicating the destination status of circuit configuration p=2. Circuit configuration p=3 is formed by link 3₅ between nodes 2₂ and 2₃ and link 3₆ between nodes 2₂ and 2₅ (FIG. 4C). A table 12C contains a list of codes C_(3n) for the destination status of circuit configuration p=3. Circuit configuration p=4 is formed by link 3₄ between nodes 2₁ and 2₄ (FIG. 4D). A list of codes C_(4n) for the destination status of circuit configuration 4 is given in table 12D. Circuit configuration p=5 is formed by link 3₈ between nodes 2₃ and 2₅ (FIG. 4E). A list of codes C_(5n) for the destination status of circuit configuration 5 is given in table 12E. Circuit configuration p=6 is formed by link 3₁ between nodes 2₁ and 2₃. (FIG. 4F). A list of codes C_(6n) for the destination status of circuit configuration 4 is given in table 12F. Finally, circuit configuration p=7 is formed by link 3₉ between nodes 2₁ and 2₅ (FIG. 4G). A list of codes C_(7n) for the destination status of circuit configuration p=7 is given in table 12G. Tables 12A-12G are stored in memory 7.

FIG. 5 is a flowchart describing a sequence of programmed instructions which are executed by network controller 5 according to one embodiment of the present invention for deriving network configuration data N_(mn) from the circuit status bits E_(mp) and destination status code C_(pn) just described. Network configuration data N_(mn) is represented as follows: ##EQU1##

The program is activated in response to a signal from management console 6 when a network identifier m is determined for reconfiguring an existing configuration. Program execution starts with step 20 in which variables p and n are both reset to 1. Exit then is to step 21 which directs the reading of circuit status bits E_(mp) and destination status codes C_(pn) from memory 7 using variables m, p and n as address pointers. Control proceeds to step 22 in which circuit status bits E_(mp) are multiplied with destination status codes C_(pn). Assume that if m is determined to be equal to 1, E₁₁ and C₁₁ are fetched from memory 7 and multiplied together to produce a product N_(mn)(1). Since E₁₁ =1 and C₁₁ =01000, N₁₁(1) is equal to 01000 (see FIGS. 2 and 4A). Control advances to step 23 to store N_(mn)(p) into memory 7, and moves to decision step 24 to determine if p is equal to the total number of the circuit configurations, i.e., 7. If the answer is negative, control goes to step 25 in which p is incremented by 1, with control returning to step 21 to repeat steps 22 and 23. Therefore, in the second pass through steps 22 and 23, N₁₁(2) =E₁₂ ×C₂₁ =1×00000=00000 is obtained (FIGS. 2 and 4B). In this way, the following relations are obtained for switching node 2₁ as steps 22 and 23 are executed seven times:

N₁₁(1) =E₁₁ ×C₁₁ =1×01000=01000 (FIGS. 2, 4A)

N₁₁(2) =E₁₂ ×C₂₁ =1×00000=00000 (FIGS. 2, 4B)

N₁₁(3) =E₁₃ ×C₃₁ =0×00010=00000 (FIGS. 2, 4C)

N₁₁(4) =E₁₄ ×C₄₁ =0×00010=00000 (FIGS. 2, 4D)

N₁₁(5) =E₁₅ ×C₅₁ =0×01010=00000 (FIGS. 2, 4E)

N₁₁(6) =E₁₆ ×C₆₁ =0×00000=00000 (FIGS. 2, 4F)

N₁₁(7) =E₁₇ ×C₇₁ =0×00000=00000 (FIGS. 2, 4G)

If an affirmative decision is made in step 24, control exits to step 26 to give a total (N₁₁) of the N₁₁(1) through N₁₁(7) values, which is equal to 01000. Network configuration data N₁₁ obtained at step 26 is stored into a most recent data storage location of memory 7 (step 27).

Exit then is to step 28 in which controller 5 applies N₁₁ to transmitter 8₁, which, in turn, transmits this data as a network configuration signal to switching node 2₁. Control proceeds to step 29 to reset p to 1 and moves to step 30 to check to see if n is equal to the total number of switching nodes, i.e., 5. If the answer is negative, control moves to step 31 to increment n by 1 and returns to step 21 to repeat the process for switching nodes 2₂ through 2₅ to obtain the following network configuration data N₁₂, N₁₃, N₁₄ and N₁₅. ##EQU2##

If the decision is affirmative at step 30, control terminates the program execution.

Therefore, network configuration signals N₁₂ through N₁₅ are transmitted to switching nodes 2₂ ˜2₅, respectively, from transmitters 8₂ ˜8₅, to configure the communications network as shown in FIG. 7A, which is a combination of circuit configurations p=1 and p=2. A list of network configuration data N₁₁ ˜N₁₅ is tabulated as shown in a table 13A.

It is seen that the amount of data to be stored in network management memory 7 is significantly reduced and hence a wide range of network configurations can be accommodated, providing a high level of system flexibility.

FIG. 6 is a flowchart according to another embodiment of this invention, in which network configuration data for networks with identifiers m=1 through m=5 are prepared in advance and stored in memory 7 for later retrieval. Program execution begins with step 40 which initializes variables m, p and n by resetting them each to 1. Exit then is to step 41 to read E_(mp) and C_(pn), using variables m, p and n as address pointers. Data E_(mp) and C_(pn) are then multiplied together to obtain N_(mn)(p) (step 42), which is stored into memory 7 (step 43). Variable p is checked to see if p =7 (step 44). If the answer is negative, p is incremented by 1 (step 45) and steps 41 to 43 are repeated, so that N₁₁(1) through N₁₁(7) are stored into memory 7.

With the answer being affirmative in step 44, control exits to step 46 to give a total sum N₁₁ of the N₁₁(1) through N₁₁(7) values. Exit then is to step 47 to store N₁₁ into memory 7 as network configuration data for switching node 2₁. Variable p is then reset to 1 (step 48) and variable n is checked to see if it equals the total number of switching nodes (step 49). If the answer is negative, n is incremented by 1 (step 50) and steps 41 through 48 are repeated for switching nodes 2₂ through 2₅. In this way, N₁₁ through N₁₅ are stored in memory 7 as table 13A (FIG. 7A) for a network configuration m=1.

Exit then is to step 51 which checks to see if m=5. If the answer is negative, m is incremented by 1 (step 52), and steps 41 to 49 are repeated again to produce N₂₁ through N₂₅ for switching nodes 2₁ through 2₅, respectively, which are connected in a network configuration identified with m=2, which is formed by circuit configurations 1 and 3.

More specifically, network configuration data N₂₁ through N₂₅ are obtained by the following calculations and stored in table 13B (FIG. 7B): ##EQU3##

With m=3, network configuration data N₃₁ through N₃₅ are obtained by the following calculations, and stored in table 13C (FIG. 7C): ##EQU4##

With m=4, network configuration data N₄₁ through N₄₅ are obtained by the following calculations, and stored in table 13D (FIG. 7D): ##EQU5##

With m=5, network configuration data N₅₁ through N₅₅ are obtained by the following calculations, and stored in table 13E (FIG. 7E): ##EQU6##

FIG. 8A is a flowchart according to a second embodiment of the present invention, which is intended to reduce the burden of the switching nodes during system reconfiguration phases by transmitting new network configuration data to those nodes requiring reconfiguration, rather than transmitting them to all switching nodes. If a new network reconfiguration request is made, the program starts with operations step 60 which directs the moving of network configuration data N_(mn), pertaining to the existing network, to a new location of memory 7. Exit then is to step 61 which directs the setting of variable m to the new network identifier (j). Subroutine 62 follows, which directs the executing of the steps of FIG. 5 by skipping step 28 as indicated by line 32 (FIG. 5) to obtain new network configuration data N_(jn). Control exits to step 63 to set variable n equal to 1. Exit then is to step 64 to read existing network configuration data N_(mn) and new network configuration data N_(jn). Modulo-2 summation is performed bit-by-bit between data N_(mn) and N_(jn) to produce a differential signal S_(n) (step 65). Control proceeds to step 66 to check to see if S_(n) is equal to zero. If the answer is affirmative, control exits to step 68 and, if negative, moves to step 67 to send the new network configuration data N_(jn) to switching node 2_(n). Step 68 is then executed by checking to see if n=5. If the answer is negative, variable n is incremented by 1 (step 69) to repeat the process until n=5. Therefore, new network configuration data are sent to those switching nodes needing reconfiguration.

The amount of data to be transmitted during network reconfiguration phases can be further reduced by transmitting to those switching nodes requiring network reconfiguration data bits pertaining only to the routes or destinations of such nodes where changes are to be effected. The instructions shown in FIG. 8B are generally similar to those of FIG. 8A except that step 67 of FIG. 8A is replaced with step 67A. Following a decision that S_(n) is not equal to 0 (step 66), exit is to step 67A in which all bits of differential data S_(n) are searched for a binary "1" which indicates that a route change is to be effected. Bit position data representative of the bit positions in which a binary "1" is detected are transmitted via transmitter 8_(n) to switching node 2_(n). On receiving the bit position data, switching node 2_(n) checks it against the current states of the links (routes). If the link specified by the bit position data is a regular (currently active) link, it is disconnected from the network and put into the list of spare links. If the specified link is in the list of spares, it is established as a regular link and stricken from the list of spare links.

FIG. 9A is a flowchart according to a modified form of the second embodiment of this invention. According to this modification, network configuration data prepared according to the flowchart of FIG. 6 are utilized for subsequent network reconfigurations.

The program of FIG. 9A is executed in response to a command input indicating a new network identifier. In step 70, variable m is set equal to the identifier of the existing network and variable j is set equal to the new network identifier. Variable n is set to 1 (step 71), and existing and new network configuration data N_(mn) and N_(jn) are recalled from memory 7 (step 72). Modulo-2 summation is performed bit-by-bit between data N_(mn) and N_(jn) to produce a differential signal S_(n) (step 73). Control proceeds to step 74 to check to see if S_(n) is equal to zero. If the answer is affirmative, control exits to step 76 to store N_(jn) into memory, and if negative it moves to step 75 to send new network configuration data N_(jn) to switching node 2_(n). Step 77 is then executed by checking to see if n=5. if the answer is negative, variable n is incremented by 1 (step 78) and control returns to step 72, to repeat the process until n= 5.

The program of FIG. 9A is modified as shown in FIG. 9B, which is similar to FIG. 9A, with the exception that step 75 of FIG. 9A is replaced with step 75A which is identical to step 67A of FIG. 8B. Following a decision that S_(n) is not equal to 0 (step 74), exit is to step 75A in which all bits of differential data S_(n) are searched for a binary "1" which indicates that a route change is to be effected. Bit position data representative of the bit positions in which a binary "1" is detected are transmitted via transmitter 8_(n) to switching node 2_(n). On receiving the bit position data, switching node 2_(n) checks it against the current states of the links (routes). If the link specified by the bit position data is a regular (currently active) link, it is disconnected from the network and put into the list of spare links. If the specified link is in the list of spares, it is established as a regular link and stricken from the list of spare links

The foregoing description shows only preferred embodiments of the present invention. Various modifications are apparent to those skilled in the art without departing from the scope of the present invention which is only limited by the appended claims. Therefore, the embodiments shown and described are only illustrative, and not restrictive. 

What is claimed is:
 1. In a communications system having a plurality of switching nodes each being capable of establishing and removing relatively static connections between transmission links in response to network configuration signals and of establishing relatively dynamic connections through the established static connections in response to information pertaining to call-by-call connection requests from user terminals, a network controller comprising:memory means for storing a plurality of network configuration data corresponding respectively to distinct network configurations of said communications system, said network configuration data indicating presence or absence of transmission links from each of said switching nodes to possible destination nodes; control means for retrieving, from said memory means, first and second network configuration data corresponding respectively to an existing network configuration of said communications system and a new network configuration of said communications system, and determining if there is a difference between said first and second network configuration data; and means for transmitting said second network configuration data to selected ones of said switching nodes as said network configuration signals if said control means determines that there is a difference between said first and second network configuration data.
 2. A network controller according to claim 1, wherein said transmitting means transmits said second network configuration data only to said selected ones of said switching nodes that are connected to different destination nodes in said new network configuration than in said existing network configuration.
 3. In a communications system having a plurality of switching nodes each being capable of establishing and removing relatively static connections between transmission links in response to network configuration signals and of establishing relatively dynamic connections through the established static connections in response to information pertaining to call-by-call connection requests from user terminals, and a network control center having a memory for storing a plurality of network configuration data corresponding respectively to distinct network configurations of said communications system, said network configuration data indicating presence or absence of transmission links from each of said switching nodes to possible destination nodes, a method comprising the steps of:a) retrieving, from said memory, first and second network configuration data corresponding respectively to an existing network configuration of said communications system and a new network configuration of said communications system; b) determining if there is a difference between said first and second network configuration data; and c) transmitting said second network configuration data from said network control center to selected ones of said switching nodes as said network configuration signals if the step (b) determines that there is a difference between said first and second network configuration data.
 4. A method according to claim 3, wherein the step c) only transmits said second network configuration to said selected ones of said switching nodes that are connected to different destination nodes in said new network configuration than in said existing network configuration. 